The present invention relates to a semiconductor memory device, and more particularly to a voltage regulator which is used in a semiconductor memory device and has an adaptive bandwidth.
Semiconductor memory devices are used in various fields. Typically, semiconductor memory devices are used to store a variety of data. Semiconductor memory devices are required to have a high capacity, a high operating speed, a small size, and a low power consumption because semiconductor memory devices are used in various portable devices, such as desktop computers or notebook computers.
In a synchronous clock system requiring a high operating speed, it is important to reduce jitter of a clock tree. The clock tree represents a multi-stage buffering unit disposed between a clock source and a latch in order to control a delay of a clock reaching latches inside a chip receiving the clock from the clock source. The clock tree is used in a CPU or a controller, as well as in a semiconductor memory device, which is a synchronous clock system using a clock.
In the case of the system using the clock tree, jitter of the clock tree is often generated according to noise included during the supply of power, degrading the performance of the system.
In order to reduce the jitter of the clock tree, a voltage regulator is used for separating the power of the clock buffer from noise environments. The voltage regulator can reduce jitter by reducing the noise from the supplied power.
However, the use of a voltage regulator has the following problems. Bands of frequency components are different in each supplied power, and resonance frequencies of the voltage used to generate a system clock are different. In this case, the frequency component of the supplied voltage is different from that used to generate the system clock. Thus, interference between frequencies and noise is increased. Even though a voltage regulator is used, noise is not almost reduced due to interference between frequencies. Therefore, the efficiency that can be obtained from a voltage regulator is much degraded.